Pyrites
2 of the 6 encyclopedias on this shelf carry an entry for Pyrites. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
pi-ri'tez, a common mineral consisting of one atom of iron to two atoms of sulphur. It is brass-yellow in color. When rubbed like a pencil, it makes a greenish-black streak. From its appearance it is called fool's gold. The early explorers of Virginia took home shiploads of iron pyrites under the impression that they were carrying gold. When roasted it gives off a smell of sulphur. This is the miner's test. Owing to the presence of sulphur, pyrites is used largely in the manufacture of sulphuric acid. It is obtained in commercial quantities in various localities from Maine to Georgia. It abounds in the Rocky Mountain region. Old World supplies are found at Rio Tinto in Spain, Avoca, Ireland, and elsewhere. Sometimes the mineral occurs in the form of beautiful crystals. Fine specimens are found in the Isle of Elba; Cornwall, England; Peru; Chester County, Pennsylvania; and Central City, Colorado. Nodules of pyrites, found in the chalk beds of western Europe, were employed instead of flint. The French called it the musket stone. The term pyrites is a Greek word, meaning fire. Bits found in prehistoric dwellings indicate that primitive men used it to produce fire. The old saying, "as worthless as fool's gold," hardly holds true. Several million dollars' worth are mined annually for the sake of the sulphuric acid obtained. The name pyrites is applied also to compounds of sulphur with copper, cobalt, nickel, and arsenic.
Collier's New Encyclopedia (1921)
an isometric mineral occurring frequently crystallized, also massive, in mammillary forms with fibrous structure, and stalactitic with crystalline surface. Occurs abundantly distributed in rocks of all ages, either as crystals, crystal-grains, or nodules, also in metalliferous veins.
What Has Changed in the Last Century
Aiton's claim in 1910 that "several million dollars' worth are mined annually for the sake of the sulphuric acid" describes an industry that has largely vanished. Since the mid-20th century most of the world's sulphur has come not from roasting pyrites but from sweetening sour natural gas and refining crude oil by the Claus process, which yields elemental sulphur as a by-product; pyrite roasting survives on a large scale mainly in China. The mineral's modern notoriety is environmental rather than commercial: when pyrite in mine waste and exposed rock oxidises it produces sulphuric acid in place, and acid mine drainage is now one of the most expensive legacies of historic metal mining, including at Rio Tinto in Spain, which both entries name as a great source. Neither account could mention that iron pyrite is now studied as a cheap semiconductor for solar cells, or that its microscopic forms and sulphur isotopes are used to reconstruct oxygen levels in ancient oceans.
Written for this edition, 2026.